Field of the Invention
Optimally cost-beneficial and dependable transmission systems are desirable for the transmission of digital signals. Ring structures are preferably employed for the connection of the individual network elements (network nodes/terminals, terminal multiplexers, add/drop multiplexers) since this structure makes it possible to conduct xe2x80x9cworking signalsxe2x80x9d and xe2x80x9cprotection signalsxe2x80x9d on separate paths (i.e., to respectively connect two network elements to one another via the shortest ring section with working channels, as a rule, and to connect them to one another via the longer ring section with protection channels, at least in the case of malfunctions). The protection connection is automatically produced given line interruptions, so that only brief disturbances occur.
Given higher data rates, as employed in the synchronous digital hierarchy (SDH) or the synchronous optical network (SONET), optical fibers are utilized because of the greater transmission bandwidth and their lower attenuation. The wavelength-division multiplex method is often employed in order to optimally utilize the optical fibers. Patent applications DE 43 37 089 A1, EP 651 529 A1 and EP 0651 528 A1 disclose optical ring networks wherein different wavelengths are employed for the connections of network elements in a ring.
The contribution, xe2x80x9cFirst results of an experimental Coloured Section Ringxe2x80x9d, in the 22nd European Conference on Optical Communicationxe2x80x94ECOC""96, Oslo, WeB.2.3, page 3.51 through page 3.54, describes a ring structure shown in FIG. 1, whereby neighboring add/drop multiplexers are connected to one another via two respective waveguides. Only one wavelength is used for both transmission directions between two neighboring add/drop multiplexers However different wavelengths are used on all transmission sections. The output and input and of signals ensues via optical add/drop multiplexers, that correspond to optical filters. When the working channel that usually uses the shortest ring section is disturbed, a protection connection is set up via the longer ring section using the same wavelength (i.e., the working signal previously sent via the disturbed section is xe2x80x9clooped backxe2x80x9d). Just as many protection channels as working channels with a corresponding bandwidth are required in this method. A method based on this principle is disclosed in the earlier application DE 19 707 056 A1.
An object of the invention is to optimally utilize the transmission capacity of a ring network equipped with a protection means.
According to one aspect of the invention, a method is provided for transmitting data in a bi-directional working channel between a plurality of terminals of a optical ring network that affords a protection connection. This connection is established when a disturbance of data transmission occurs via the undisturbed section of the optical ring network by utilization of a wavelength-division multiplex method executed in the working channel, wherein a single bi-directional protection channel is comprised of a predetermined wavelength range in at least a transmission capacity of the working channel for connecting all of the plurality of terminals to one another. The method includes detecting whether at least one of a disturbance of a line section between two neighboring terminals for a malfunction of a working line/trunk assembly of the two neighboring terminals has occurred. A protection connection is then established in the bi-directional protection channel between the two neighboring terminals via protection line/trunk modules and the undisturbed sections of the optical ring network when either of the disturbance or malfunction conditions has occurred. Hence, a protection channel is established that loops through the unaffected terminals of the plurality of terminals.
According to another aspect of the invention, an apparatus is provided for transmitting data between a plurality of terminals in an optical ring network that provides protection when data transmission is disturbed through enabling a protection connection using wavelength division multiplexing in a protection channel via undisturbed sections of the optical ring network. The apparatus includes a plurality of wavelength-division multiplexers and demultiplexers for decoupling and coupling individual working and protection signals, respectively. A single bi-directional channel is comprised of predetermined wavelength range and at least the transmission capacity of the working channels to connect all of the plurality of terminals to one another. Also, corresponding working and protection line/trunk modules for each transmission direction are provided in each of the network terminals. Further, a plurality of optical switches are disposed between the outputs of the wavelength-division demultiplexers and inputs of the wavelength-division multiplexers and are configured to loop the protection channel through the plurality of terminals when there are no disturbed connections and, alternatively, for switching onto an allocated protection module and producing a protection connection with the bi-directional protection channel via undisturbed sections of the optical ring network when a disturbance has occurred.
Only one protection channel to which all terminals have access (ie., can send and receive data) is provided in the invention. In the undisturbed case, the channel is through-connected from all terminals, whereas, in case of malfunction, a connection is set up between the affected channels via the undisturbed, longer ring section. Like the working channel, the protection channel can also comprise a plurality of sub-channels with a plurality of wavelengths that set up connections to different terminals. In the protection case, connections are then set up with different wavelengths via the allocated sub-channels.
The dependability of a ring network is increased in that separate working and protection line/trunk modules are provided. The working signals and the protection signals are simultaneously checked in order to prevent unnecessary switching given protection connections,that are likewise disturbed.
Good dependability with low outlay is achieved when a faulty transmission channel caused, for example, by a channel break and a faulty line/trunk module are treated the same. In both instances, a switch is simultaneously made onto the protection line/trunk module and the protection connection.
Enhanced security is achieved by employing an additional switching module that, given a malfunctioning working line/trunk module, switches onto the corresponding protecting line/trunk module without a simultaneous switch onto the protection connections. Thus protection channel is available for the protection connection in line transmissions despite malfunctioning line/trunk modules.
The operating dependability can be further increased doubling the terminal equipment (multiplexers and line/trunk modules) and by a corresponding switching means.
Additional advantages and novel features of the invention will be set forth, in part, in the description that follows and, in part, will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.